AuditEntryItem

// The namespace is different because the https://bulk-operations.net/ library is used under the hood.
namespace Z.BulkOperations
{
    /// <summary>The `AuditEntryItem` class represents the auditing value metadata of a row that has been modified. The entry item is used in the [AuditEntry](audit-entry) class.</summary>
    public class AuditEntryItem
    {
        /// <summary>Gets or sets the `ColumnName` property.</summary>
        public string ColumnName { get; set; }

        /// <summary>Gets or sets the `NewValue` property. The `NewValue` is the actual value after an insert or an update operation is executed.</summary>
        public object NewValue { get; set; }

        /// <summary>Gets or sets the `OldValue` property. The `OldValue` is the previous value before an update or a delete operation is executed.</summary>
        public object OldValue { get; set; }
    }
}

// Execute
List<AuditEntry> auditEntries = new List<AuditEntry>(); 
connection.UseBulkOptions(options => 
{ 
    options.UseAudit = true;
    options.AuditEntries = auditEntries; 
})
.BulkMerge(list); 

// Result
FiddleHelper.WriteTable("1 - AuditEntry", auditEntries);
FiddleHelper.WriteTable("2 - AuditEntryItem", auditEntries.SelectMany(x => x.Values));